Currently, medical imaging techniques as such Magnetic Resonance Imaging (MRI), also known as nuclear magnetic resonance imaging (NMRI) or magnetic resonance tomography (MRT), are not applicable to patients with cardiac implant devices: partly because the myocardial scar (viability) imaging using late gadolinium enhancement MRI, which is a clinical gold standard for myocardial tissue characterization, are often nondiagnostic due to the presence of these devices.
Late gadolinium enhancement (LGE) cardiac MRI plays an important role in diagnosis and treatment of myocardial diseases. It is the clinical “gold standard” for non-invasive myocardial tissue characterization. Assessment of presence/absence, location, size and pattern of myocardial scar using LGE MRI is often the only non-invasive means of accurately diagnosing and differentiating various forms of non-ischemic cardiomyopathy, including myocarditis, arrhythmogenic right ventricular dysplasia, amyloidosis, and sarcoidosis. LGE MRI also plays an increasingly important role in guiding catheter ablations, a widely used treatment procedure for ventricular tachycardia (VT) and recurrent implantable cardioverter-defibrillator (ICD) therapies. For this procedure, the assessment of myocardial scar location, size and transmurality provided by LGE MRI allows more accurate identification of arrhythmogenic substrate and ablation sites, thereby potentially decreasing procedure time and increasing success rate.
Despite the important role of LGE MRI and the large number of patients for whom an LGE cardiac MRI could provide a non-invasive means of establishing diagnosis and guiding treatment, many of the patients do not undergo cardiac MRI due to prior implantation of cardiac devices. It has been estimated that up to 75% of patients who could benefit from LGE MRI are recipients of cardiac devices, such as implantable cardioverter defibrillators (ICD) and cardiac pacemakers (PM). Presence of cardiac devices are traditionally considered a contraindication for cardiac MRI. Potential risks of MRI for patients with ICDs or pacemakers include heating of the tissue adjacent to lead electrodes, mechanical forces and vibration, induction of arrhythmias, and alteration of device function. Numerous recent studies have demonstrated that it is safe to scan patients with cardiac devices who are not device dependent and have no abandoned leads if certain precautions are taken, including pre- and post-MRI interrogation of the device. In the United States, approximately 116,000 ICDs and 397,000 cardiac pacemakers were implanted in 2009. MRI of patients with implanted devices has been reported to be performed safely for most patients whose rhythms are not device dependent.
While these recent advances in MRI safety are encouraging, the diagnostic value of the LGE images for these patients, however, is often severely limited by significant imaging artifacts that arise from the device generator, a metal box that is implanted predominantly on the upper-left side of the patient's chest. The device generator results in multi-kHz off-resonance within myocardial tissue and typically causes hyper-intensity image artifacts in LGE images, which can appear similar to the hyper-enhancement of scar tissue (see, e.g., FIG. 1). A recent study has shown that these artifacts typically occur at regions of the heart that are close to the device generator, such as left ventricular (LV) apex, lateral wall, and outflow track. Artifacts due to the device also appear in cine and perfusion CMR images, but these are not as severe as those in LGE images. Additional MRI signal artifacts due to off-resonance, including image distortions, signal pile-up and signal voids are also a potential concern.
These bright-signal imaging artifacts have been previously reported; however, there has been no study to date that investigated the origin of the artifacts or proposed a solution to address this important issue.
What is needed are systems and methods that can overcome the deficiencies in the art.